Versatile traction systems that permit movement on various different terrains are required for a number of different purposes. A particular example is a wheelchair. In most wheelchairs the traction system consists of wheels (typically one main, large wheel and one auxiliary, small wheel on each side) and it permits to move the wheelchair over smooth horizontal surfaces of such floors or pavements. These traction systems are not suitable for passing obstacles such as steps and others, moving through staircases or moving over rough terrains. A versatile traction system has been described in PCT Publication WO 99/21740. In the system described in this publication, means are provided that can change at will the traction configuration for the purpose of increasing the trafficability and safety. A preferred use of the system described in this PCT publication is wheelchairs.